The accurate timing of the excitation of phases with respect to rotor position, in a switched reluctance motor, may be an important factor to obtain optimal performance. Rotor position sensors may be widely used in switched reluctance motors for monitoring rotor position. Such monitoring may be conventionally performed by an optical or magnetic sensor detecting a feature mounted on the rotor or motor shaft. Control of the rotor position in the reluctance motor may be based on data relating to the rotor position.
To avoid dependency upon sensors, sensorless monitoring and control methods have been developed. Sensorless monitoring methods of switched reluctance motors may include signal injection methods and direct phase measurement methods.
Signal injection methods may rely on diagnostic energisation pulses, for example non-torque producing pulses, that allow the controller to monitor the diagnostic current and accordingly the variation in inductance, from which the rotor position can be computed. In general, signal injection methods may be useful at starting and low operating speeds, but may adversely impact the motor performance at higher operating speeds.
Direct phase measurement methods may rely on monitoring phase current and voltage in order to determine the rotor position. A direct phase measurement method may use the concept of phase current freewheeling. Phase current freewheeling may be produced in a switched reluctance motor by setting voltage across a phase winding to zero for a period of time. During the freewheeling period current may circulate around the winding and the flux may be constant.
EP0780966B1 describes a method of sensorless rotor position monitoring in reluctance machines. The method comprises determining the rate of change of current at a particular point at which current in the winding may be arranged to freewheel. The point may coincide with alignment of a rotor and a stator pole such that the rate of change of current is predicted to be zero. The magnitude and polarity of any variation from the predicted rate of change may indicate a rotor position not in alignment with the actual rotor position and whether it is in advance of, or retreated from, the predicted position.
EP2712075 discloses a method to control the rotor position in a reluctance machine. The method involves energising the phase winding so to move the rotor relative to the stator, freewheeling current through the phase winding over a freewheeling period, sampling rate of change of phase current and amplitude of phase current, de-energising the phase winding and computing the angular position of the rotor.
The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of the prior art system.